1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for attaching information on an image to be printed.
2. Description of the Related Art
In recent years, an image processing method has been widely used, in which embedding information is converted into code information (coded information) that requires some decoding processing, and is printed on print media. Generally, the code information is embedded in two-dimensions on images, and referred to as two-dimensional code.
A user cannot recognize the printed code information without performing some processing. That is, the user can recognize the code information by reading the code information as image data using a reading device and performing appropriate decoding processing on the image data.
Typically, in the decoding processing, the read image data is transferred to a computer and decoded by an application program that runs on the computer. However, a method for decoding is not limited to the above one. For example, as in a case of two dimensional code compatible mobile phones, the decoding processing can be performed in the reading device, or the decoding processing can be performed in copying machines that have multiple functions.
The two-dimensional code is roughly categorized into high-density code information and low-density code information. The high-density code information is prepared independent of characters or patterns (print information) that are printed on paper and is embedded, for example, on four corners of the paper. For example, bar codes are used in the high-density code information.
On the other hand, the low-density code information is superimposed on the characters or patterns and printed, for example, over the entire paper.
The low-density code information is represented using a dot array, and the information amount that can be embedded in a predetermined area on paper is relatively small. However, the density of lines or dots representing the information can be reduced. As a primary advantage of attaching the low-density code information on the paper, it is not necessary to prepare a particular space for printing the code information.
On the other hand, in the case of the high-density code information, the density of the lines or dots for representing the information is higher. Therefore, if the code information is superimposed, the print information under the code information may be lost. Accordingly, to prevent the print information from being lost by attaching the code information, it is necessary to keep in advance a space where the code information is to be attached and attach the code information in the predetermined space.
On the other hand, generally, in the case of the low-density code information, even if the code information is attached, the legibility can be maintained although some information deteriorates, and the information can be possibly maintained. Accordingly, it is possible to superimpose the low-density code information on the print information without losing the print information. That is, design flexibility of print information is increased since there is no need for preparing a particular space for attaching the low-density code information. However, the low information density can be compensated for by using a large print area.
As a second advantage of attaching the low-density code information to paper, it is difficult to remove the code information. In the attaching method of this type, the print information and the code information are inseparably printed, and it is extremely difficult to remove only the code information and copy only the print information. Accordingly, for example, “print attributes” such as information about the printer that performed the printing, information about the user who did the printing or the print date and time, can be printed as the low-density code information on a print material. Therefore, even if the printed material is leaked to outside, the leakage route can be readily detected.
In a case where the code information is used for a security purpose, there is a problem in attaching information when a copy is made. When an original document on which print attributes are attached for security purposes is copied, it is necessary to further attach print attributes in the copying.
Japanese Patent Application Laid-Open No. 2003-094734 discusses a technique for providing in advance a space to which attaching information is added, and for storing information (write history information) for indicating its location. When the code information is attached, the write history information is read and a location for attaching the code is detected based on the read information. Then, the code information can be attached.
The above attaching method can be applied to high-density code information, but cannot be applied to the method for attaching low-density code information which is embedded over a large part of the paper. Because a large space on the paper is used for the first attaching of the low-density code information, it is difficult to provide a space for attaching the additional information. Moreover, even if the space for attaching the additional information is provided, the attaching part is separated from the code information attached in the first printing. Accordingly, the security level is lowered.